72 Br. F. A. Bather — Notes on Yunnan Cystidea. 



All those in which the epithecal food-grooves do not extend beyond 

 the adoral circlet of plates are referred to the Sphseronidse. The 

 line between the Sphseronidse and the more advanced Glyptosphseridse 

 cannot he drawn rigidly, and such a genus as Proteocystis constitutes 

 a natural transition. Sinocystis, however, comes well within this 

 boundary. 



On the other side it is not easy to define the limit between the 

 Sphseronidse and the Aristocystidse, from which, apparently, they 

 were evolved. In 1899 and 1900, accepting the statement (which 



1 was unable to disprove) that the genera referred to the latter 

 Family had no exothecal skeletal processes (e.g. brachioles), and 

 observing the irregular and apparently unspecialized arrangement 

 of their pore-canals when present, I placed the Aristocystidse in the 

 Amphoridea. Jaekel (1899) removed from the Aristocystidse all 

 the genera that I was including in that Family, with the exception 

 of Aristocystis, but added to it his new genus, Trematocystis, which 

 will be discussed in Section B. In 1906 (Palseont. Indica, n.s., II, 

 No. 3) I showed that the pores in Aristocystis dagon from Burma 

 were haplopores, that is to say not yoked in couples but isolated and 

 irregularly distributed, and that they might be connected by surface 

 channels which had a radial arrangement and crossed the sutures. 

 Consequently I was not induced to place Aristocystis with the 

 Diploporita as Jaekel had done. 



Taking Aristocystis as represented by its genotype, A. bohemica, 

 with which A. dagon is in general agreement, one notices a consider- 

 able resemblance to Sinocystis : the extended peristome and the 

 three other thecal openings occupy the same relative positions and 

 have much the same shape in the two genera. The genera are 

 distinguished by their pores, and by the less development of the 

 brachiole-facets in Aristocystis. One would take Sinocystis to be 

 derived from Aristocystis, but there. is the possibility that Jaekel 

 may be right in reversing the relation. Unfortunately there is at 

 present no means of settling this question by reference to strati- 

 graphical position. 



It should be remembered that the pore-structures figured by 

 Barrande for various specimens of Aristocystis fall into two 

 categories. The pores found in the typical A. bohemica seem to be 

 haplopores, united by surface-channels into series ranging from 



2 to 6 ; in this species the channels do not cross the sutures. The 

 channels are of approximately equal width throughout their length, 

 but are sinuous and irregular. In the other category the pores are 

 far more obviously in pairs, and those of each pair are connected by 

 a rather narrow channel of horse-shoe shape, at the ends of which 

 they lie (Barrande, 1887, pi. 13, figs. 4, 12, 13, 15, 18; pi. 17, 

 fig. iii, 5; pi. 14, figs. 10, 11). On quite unimportant grounds of 

 external shape, Barrande included these and other specimens in 

 A. bohemica as varieties, but he did also suggest that none of those 

 with horse-shoe channels really belonged to Aristocystis. The 

 adoral region of the theca in the latter specimens is unknown, but 

 the pore-character warrants their separation as a genus for which 

 I propose the name Hippocystis in allusion to the horse-shoe. It 

 may be left, pending further information, in the Aristocystidse. 



